The present invention relates to storage of boxes and in particular to an apparatus for locally buffering boxes (also called xe2x80x9ccarriersxe2x80x9d or xe2x80x9ccassettesxe2x80x9d) of semiconductor wafers at or near one or more processing stations in a integrated circuit fabrication system.
Integrated circuit (commonly abbreviated as xe2x80x9cICxe2x80x9d) dies are manufactured by performing a number of steps on a semiconductor wafer (also called xe2x80x9csubstratexe2x80x9d) in a fabrication system (commonly abbreviated as xe2x80x9cfabxe2x80x9d). Wafers are normally held in a central store 1 (commonly called xe2x80x9cstockerxe2x80x9d), and are transported to one or more processing stations 2A-2M (wherein Axe2x89xa6Jxe2x89xa6M, M being the total number of processing stations). During transportation, a number of wafers are held in a box 3 (also called xe2x80x9ccarrierxe2x80x9d, xe2x80x9ccassettexe2x80x9d, xe2x80x9cSMIFxe2x80x9d, xe2x80x9cboxxe2x80x9d, xe2x80x9cpodxe2x80x9d, xe2x80x9cFOUPxe2x80x9d and xe2x80x9ctransporting containerxe2x80x9d). The size of a carrier depends on the maximum number of wafers that can be held therein, and prior art discloses carriers for holding 13 wafers as well as more recent carriers for holding up to 25 wafers, or as few as one wafer.
As illustrated in FIG. 1A, a carrier 3 may be picked up from stocker 1 by an overhead vehicle 4 (commonly abbreviated as xe2x80x9cOHVxe2x80x9d), and transported to any of processing stations 2A-2M (also called xe2x80x9cprocessing systemsxe2x80x9d or xe2x80x9cprocess toolxe2x80x9d) depending on the fabrication step that is to be performed thereon. Instead of an OHV 4, carriers may also be carried manually, or alternatively by an automated guided vehicle (not shown in FIG. 1A; commonly abbreviated as xe2x80x9cAGVxe2x80x9d), by a personal guided vehicle (also not shown in FIG. 1A; abbreviated as xe2x80x9cPGVxe2x80x9d) or by a rail guided vehicle (also not shown in FIG. 1A; abbreviated as xe2x80x9cRGVxe2x80x9d).
U.S. Pat. No. 6,283,692 granted to Perlov, et al. (which is incorporated by reference herein in its entirety as background) states that xe2x80x9cIn order to ensure that the processing equipment does not sit idle, a nearly continuous supply of unprocessed substrates should be available at the processing station. Unfortunately, many processing stations can hold only a single cassette at the loading platform. Therefore, once all of the substrates in the cassette have been processed, the cassette must be quickly replaced, either manually or by an AGV, with a new cassette containing unprocessed substrates. Unfortunately, running such a just-in-time cassette inventory system requires either significant operator oversight or a large number of AGVs, thereby increasing the costs of the fabrication facility. Therefore, there is a need for a method and apparatus which continuously supplies substrate cassettes to a processing system so that system down time is reduced or eliminated.xe2x80x9d See column 1, lines 34-45.
Perlov, et al. propose xe2x80x9ca method and apparatus for storing multiple cassettes at a processing station, ensuring that a nearly continuous supply of unprocessed substrates is available for processing and that the processing equipment does not sit idle. Multiple cassettes can be stored at a processing station in a front-end support frame and a cassette can be moved to a docking station where substrates are extracted and transferred to the processing equipment. An automation system is mounted or otherwise disposed on the frame to transfer cassettes between docking stations or between processing stations. The apparatus does not increase the footprint, i.e., the required area on the cleanroom floor, of the processing station. In another aspect of the invention, cassettes can be transported between different processing stations without the use of an AGV.xe2x80x9d See column 1, lines 53-67.
Referring to FIG. 1A, after transportation, each carrier is placed on a box opener/loader 5 (also called xe2x80x9cload portxe2x80x9d or xe2x80x9cbox openerxe2x80x9d) located in front of a processing station 2A. Each box opener/loader/loader 5 opens a lid of the carrier, so that wafers inside the carrier can be extracted by a robot located in an enclosure of processing station 2A. The enclosure provides a nearly particle-free environment in which wafers may be handled, as required by, for example, International SEMATECH, located at 2706 Montopolis Drive, Austin Tex. 78741, xe2x80x9cI300I Factory Guidelines: Version 5.0xe2x80x9d (which is incorporated by reference herein in its entirety as background). See section 2.7.
Depending on the throughput of various processing stations 2A-2M and also depending on the order in which processing stations 2A-2M are used during fabrication, one, two or even four box opener/loader/loaders may be provided in front of a processing station, as illustrated in FIG. 1A. Although each box opener/loader/loader is illustrated in FIG. 1A as being capable of supporting only one carrier, it is possible for a box opener/loader/loader (also called xe2x80x9cloading and unloading stationxe2x80x9d) to support two carriers, as described by, for example, U.S. Pat. No. 5,772,386 granted to Mages et al. (which is incorporated by reference herein in its entirety as background).
In some embodiments of the invention, a store having its own footprint separate and distinct from any of the above-described items is provided locally at a processing station, for example, in a fab for integrated circuit dies. The store (also called xe2x80x9cbuffer apparatusxe2x80x9d) is located adjacent to a box opener/loader that in turn is adjacent to the processing station. The buffer apparatus transfers boxes one at a time to/from the box opener/loader that in turn opens each box and wafers therein may be transferred to/from the processing station. In such embodiments, the buffer apparatus transfers a box to/from a box opener/loader directly, without an intermediary (such as a human, an OHV, an AGV, a RGV or a PGV) between the box opener/loader and the buffer apparatus. Depending on the embodiment, the buffer apparatus may transfer boxes to/from such an intermediary (in addition to or instead of transferring the boxes to/from a box opener/loader).
One embodiment of such a stand-alone buffer apparatus includes two types of mechanisms that respectively move a box (also called xe2x80x9ccarrierxe2x80x9d) vertically and horizontally to/from a position of storage (also called xe2x80x9cstorage positionxe2x80x9d) within the apparatus. Specifically, a mechanism (hereinafter xe2x80x9cvertically moving mechanismxe2x80x9d) that is itself capable of moving vertically is fixedly attached to a foot, and in addition a number of mechanisms (hereinafter xe2x80x9chorizontally moving mechanismsxe2x80x9d) that are each capable of moving horizontally are attached to the vertically moving mechanism. Although in the just-described embodiment, a single mechanism moves all the horizontally moving mechanisms in unison during any vertical movement of a carrier, in alternative embodiments each horizontally moving mechanism may be moved vertically independent of the vertical movement of another horizontally moving mechanism.
Several embodiments of the buffer apparatus move a carrier between the above-described storage position and a predetermined position (called xe2x80x9ctransfer positionxe2x80x9d) that is located outside of the volume occupied by the buffer apparatus. The transfer position is separated from the foot in the horizontal direction by a distance called xe2x80x9chorizontal extentxe2x80x9d and in the vertical direction by another distance called xe2x80x9cvertical extent.xe2x80x9d
During a storage operation, the buffer apparatus moves a carrier from the transfer position through the horizontal extent, and thereafter moves the carrier vertically into a storage position. These acts are reversed for retrieval of a previously stored carrier. Some embodiments of the above-described buffer apparatus have another transfer position (called xe2x80x9clower transfer positionxe2x80x9d), which is in addition to the above-described transfer position (called xe2x80x9cupper transfer positionxe2x80x9d). In one such embodiment, the buffer apparatus is designed to transfer a carrier from any storage position to any transfer position. Specifically, the buffer apparatus can transfer a carrier from the lower-most storage position to the upper transfer position, and can also transfer a carrier from the upper-most storage position to the lower transfer position.
A buffer apparatus of the type described above has a number of storage positions (stacked one on top of another) at which a corresponding number of carriers may be stored. To reach a lower-most storage position, several embodiments of the buffer apparatus move a carrier vertically through one or more intermediate storage positions. In these embodiments, space used for storage of objects within such a buffer apparatus is also used for transport of objects vertically.
Dual use of the same space allows a buffer apparatus to occupy a small footprint (as compared to use of two spaces, each distinct from the other, for storage and for transport respectively, which would effectively double the footprint). The small size of the footprint of a buffer apparatus provides significant cost savings, e.g. in fabs where floor space in a cleanroom commands a premium. In one embodiment, the footprint of a buffer apparatus is made as small as possible, e.g. as small as the footprint of a box opener/loader, although in other embodiments a larger footprint box apparatus is used.
Although described in the context of a fab, such a buffer apparatus may also be used in non-fab environments, for objects other than carriers.